A magnetic stimulator used for medical treatment is a non-contact type stimulator that remarkably reduces pain compared to an electric stimulator and generates current at the affected body part using a magnetic force generated near the affected body part. Accordingly, the magnetic stimulator has attracted attention as a device capable of stimulating the surface of the skin, or a region of the brain or spinal column into which an electrode cannot be easily inserted.
Such a magnetic stimulator basically includes a capacitor for storing energy necessary for stimulation and a coil for discharging the energy to form a strong magnetic field. That is, if a short and strong current is injected into the coil, a pulse-shaped magnetic field is formed, and this time-varying magnetic field causes an eddy current in the system of a human body, thus stimulating nerves using the same principles that current, injected through an electrode, stimulates nerves in an electric nerve stimulation method.
A representative example to which the magnetic stimulator is applied is a medical instrument for treating urinary incontinence. FIG. 1 is a view showing an example of a conventional non-contact type medical instrument for treating urinary incontinence.
A process for treating urinary incontinence is described in brief. A magnetic field generation device for generating a magnetic field is arranged below a chair-shaped medical instrument, and a pulse current generates a magnetic field in a core if the pulse current is supplied to a coil wound around the core while a patient sits down on the chair. This magnetic field forms a magnetic field closed loop between both ends of the core. The affected part of the patient is placed in the middle of the closed loop, so that an eddy current is induced again at the affected part due to the magnetic field, thus electrically stimulating the affected part.
FIG. 2 is a view showing a brain stimulator as another example to which the magnetic stimulator is applied. A magnetic field generation device 132 is placed on an affected region of the brain 130 of a patient, and the brain is stimulated using a magnetic field and an eddy current in the same principles as those of the above example.
In order to generate an eddy current having an intensity sufficient to cause the magnetic stimulator to exhibit a treatment effect, a magnetic field of several tesla must be generated in the form of a pulse having a width of several hundreds of micro seconds (μs).
FIG. 3 is a circuit diagram of the power supply circuit of a magnetic stimulator proposed previously by the present applicant, which shows a circuit capable of generating the magnetic field having the above-described intensity. Hereinafter, the operation of the circuit is described.
First, if an AC power supply unit provides typical Alternative Current (AC) power Vs, such as 110V to 220V, 50 Hz to 60 Hz, a transformer T boosts the AC power. Boosted current I4 is full-wave rectified by a bridge diode B, and rectified current I1 is charged in a capacitor through a resistor R1 and a coil L1. In this case, the resistor R1 limits overcurrent of the current I1 to protect related circuits, and the coil L1 also functions to prevent overcurrent that may flow through circuits.
If the capacitor is charged to such an extent (+Vc) that the capacitor can be discharged, a switch S2 is turned on, thus starting discharging while causing high current I2 to instantaneously flow through a discharge coil L2. At the initial stage of discharging, when the voltage of the capacitor is +Vc, the current I2 flows only through the discharge coil L2, and current does not flow in the reverse direction −I1 of the current I1 because the current is interrupted by diodes, etc. The current I2 flowing through the discharge coil L2 is maximized when the voltage Vc of the capacitor is 0V. Thereafter, this energy is charged in the capacitor in the polarity −Vc opposite to the initial polarity.
During this discharging procedure, if the resistor R1 and the coil L1 do not exist, the discharge coil L2 and the bridge diode form a single closed loop, so that the current I2 is consumed as heat energy by respective devices and the resistance of a lead wire while flowing again through the discharge coil L2 through the bridge diode and the switch S2, instead of charging the capacitor in the opposite polarity. In addition, since the current flowing at that time is overcurrent occurring when current charged in the capacitor flows at a time, serious damage to the input AC power source Vs is caused through the transformer T.
However, if a coil L1 having a relatively high inductance exists in the circuit, a discharge frequency caused by the capacitor is very high, so that most current flowing through the above-described bridge diode and coil L1 is interrupted, but is charged in the capacitor in the opposite polarity −Vc. Even in the case where a resistor R1 having a relatively high resistance is used, the same effect can be obtained.
Thereafter, charges charged in the opposite polarity cause stimulation while passing again through the discharge coil L2 as a reverse current −I2. Even in this case, current I3 from a branch node “a” to the transformer may be generated, but does not flow through the transformer due to the coil L1 and/or the resistor R1, because discharge frequency is very high. Most current flows through the discharge coil L2 as a reverse current −I2, and is used to form a magnetic field in the discharge coil L2.
In the above circuit, the coil L1 is an important and essential component. Further, as described above, this coil must have an inductance much higher than that of the discharge coil L2 according to the characteristics thereof.
Because of the high inductance, the coil L1 is actually manufactured to have a relatively large size of about 10 cm×10 cm×5 cm and have a weight of 1 kg or more, so that the coil L1 is an obstruction to simplify the circuit.
Further, there is a problem that the manufacturing cost of a device greatly increases due to the coil L1.
A more serious problem is that, as shown in the drawing, since the coil L1 and/or the resistor R1 are connected in series in a power charge path, part of power is always lost in the coil and the resistor at the time of charging power. Moreover, because power lost in this way is changed into heat, problems related to heat generation and cooling caused by the heat generation become serious.
Therefore, with respect to the essential coil and/or resistor, which increase manufacturing cost and cause power loss, the necessity for variously modifying and designing the coil or resistor has been recently required, and the present invention is developed to satisfy this necessity.